NM_000520.6:c.78G>A

Variant names:

• chr15-72375895-C-T
• rs121907964
• NM_000520.6:c.78G>A

Variant summary

Our verdict is Pathogenic. Variant got 18 ACMG points: 18P and 0B. PVS1 PM2 PP5_Very_Strong

The NM_000520.6(HEXA):​c.78G>A​(p.Trp26*) variant causes a stop gained change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000205 in 1,461,872 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Pathogenic (★★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000021 (0 hom.)
• Consequence: HEXA NM_000520.6 stop_gained
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:5
• Conservation: PhyloP100: 2.13

Genes affected

HEXA (HGNC:4878): (hexosaminidase subunit alpha) This gene encodes a member of the glycosyl hydrolase 20 family of proteins. The encoded preproprotein is proteolytically processed to generate the alpha subunit of the lysosomal enzyme beta-hexosaminidase. This enzyme, together with the cofactor GM2 activator protein, catalyzes the degradation of the ganglioside GM2, and other molecules containing terminal N-acetyl hexosamines. Mutations in this gene lead to an accumulation of GM2 ganglioside in neurons, the underlying cause of neurodegenerative disorders termed the GM2 gangliosidoses, including Tay-Sachs disease (GM2-gangliosidosis type I). Alternative splicing results in multiple transcript variants, at least one of which encodes a preproprotein that is proteolytically processed. [provided by RefSeq, Jan 2016]

ENSG00000260729 (HGNC:):

HEXA-AS1 (HGNC:25810): (HEXA antisense RNA 1)

ACMG classification

Verdict is Pathogenic. Variant got 18 ACMG points.

• PVS1: Loss of function variant, product does not undergo nonsense mediated mRNA decay. Variant located near the start codon (<100nt), not predicted to undergo nonsense mediated mRNA decay. There are 28 pathogenic variants in the truncated region.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 15-72375895-C-T is Pathogenic according to our data. Variant chr15-72375895-C-T is described in ClinVar as [Pathogenic]. Clinvar id is 3911.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
HEXA	NM_000520.6	c.78G>A	p.Trp26*	stop_gained	Exon 1 of 14	ENST00000268097.10	NP_000511.2
HEXA	NM_001318825.2	c.78G>A	p.Trp26*	stop_gained	Exon 1 of 14		NP_001305754.1
HEXA	NR_134869.3	n.120G>A		non_coding_transcript_exon_variant	Exon 1 of 11
HEXA-AS1	NR_027262.1	n.-218C>T		upstream_gene_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
HEXA	ENST00000268097.10	c.78G>A	p.Trp26*	stop_gained	Exon 1 of 14	1	NM_000520.6	ENSP00000268097.6
ENSG00000260729	ENST00000379915.4	n.78G>A		non_coding_transcript_exon_variant	Exon 1 of 16	2		ENSP00000478716.1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000205 AC: 3 AN: 1461872 Hom.: 0 Cov.: 31 AF XY: 0.00000138 AC XY: 1 AN XY: 727234

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00000270

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:5

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Tay-Sachs disease Pathogenic:5

Mar 17, 2017

Natera, Inc.

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: clinical testing

- -

Oct 31, 2022

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

For these reasons, this variant has been classified as Pathogenic. This sequence change creates a premature translational stop signal (p.Trp26*) in the HEXA gene. It is expected to result in an absent or disrupted protein product. Loss-of-function variants in HEXA are known to be pathogenic (PMID: 1833974, 8490625). This variant is not present in population databases (gnomAD no frequency). This premature translational stop signal has been observed in individual(s) with Tay-Sachs disease (PMID: 1833974, 21967858, 25606403). ClinVar contains an entry for this variant (Variation ID: 3911). -

Jul 17, 2020

Breakthrough Genomics, Breakthrough Genomics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This variant was previously reported in individuals affected with Tay-Sachs disease in homozygous or compound heterozygous state and reported as a disease-causing mutation. [PMID: 1833974, 8257995, 21967858, 25606403] -

Jan 01, 1993

OMIM

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: literature only

- -

Jun 04, 2018

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: HEXA c.78G>A (p.Trp26X) results in a premature termination codon, predicted to cause a truncation of the encoded protein or absence of the protein due to nonsense mediated decay, which are commonly known mechanisms for disease. Truncations downstream of this position have been classified as pathogenic by our laboratory (eg. c.1168C>T, p.Gln390X; c.1274_1277dupTATC, p.Tyr427fsX5). The variant was absent in 121186 control chromosomes. c.78G>A has been reported in the literature in individuals affected with Tay-Sachs Disease. These data indicate that the variant is likely to be associated with disease. At least one publication reports experimental evidence evaluating an impact on protein function. The most pronounced variant effect results in <10% of normal activity. No clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014. Based on the evidence outlined above, the variant was classified as pathogenic. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.63	D
BayesDel_noAF	Pathogenic	0.56
CADD	Pathogenic	38
DANN	Uncertain	0.99
Eigen	Pathogenic	0.91
Eigen_PC	Pathogenic	0.75
FATHMM_MKL	Pathogenic	0.97	D
Vest4		0.74
GERP RS		4.7
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.7

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.0		Details are displayed if max score is > 0.2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Other links and lift over

dbSNP: rs121907964; hg19: chr15-72668236;